Deep sleep may hold health answers

February 15, 2006|TINA HESMAN St. Louis Post-Dispatch

Hummingbirds do it. Bears do it. Even whistle pigs do it. So why don't we do it? That's the question scientists who study hibernation are asking. If humans could hibernate, or at least harness the power of torpor (as scientists call the dormant drowse), conditions such as Sudden Infant Death Syndrome (SIDS), obesity and diabetes might be a thing of the past. Researchers hope that studies of hibernators also may aid trauma victims, help preserve transplant organs, lead to safer weight-loss treatments and blood-thinning agents and shed light on some of the most basic, but still mysterious, processes in the body. Feb. 2, the groundhog Punxsutawney Phil, aroused from his long winter's sleep, saw his shadow, and predicted six more weeks of winter. (NOTE: The calendar agrees with Phil. The official start of spring, March 21, is always a little more than six weeks away from Groundhog Day.) It's not Phil's powers of meteorological prognostication that interest scientists. Physiologists are far more concerned with the furry weatherman's sleep habits. Hibernation is an amazing feat of body regulation. Groundhogs, also known as woodchucks and whistle pigs, and their brethren in the squirrel family, are among the "true hibernators." The family includes groundhogs, their cousins the marmots, ground squirrels, prairie dogs and chipmunks. Most members hibernate or go into torpor, a suppressed metabolic state just shy of deep hibernation. The animals bulk up in the summer -- often doubling their weight -- and then go dormant through the winter. During the downtime, the hibernators stop eating and switch their metabolisms to burn fat instead of carbohydrates and protein. Their hearts slow, their breathing is altered and their body temperature drops to a degree or two above outside temperatures. Some ground squirrels can regulate their thermostats down to minus three degrees Celsius (yes, below freezing), said Steve Swoap, a physiologist at Williams College in Williamstown, Mass. Most hibernators don't dip that far, Swoap said. The way marmots monitor their fat stores could hold lessons for human dieters. Marmots "are the ultimate yo-yo dieters," said Greg Florant, a biology professor at Colorado State University in Fort Collins. Yellow-bellied marmots may enter their burrows in the fall carrying 30 percent to 40 percent of their body weight in fat. They emerge in the spring svelte with near zero body fat, he said. People who undergo such massive weight changes may suffer severe health problems, but hibernators show no ill effects. Fat is probably the key to triggering hibernation, Florant and Swoap say. Both have evidence that an appetite- suppressing hormone called leptin is involved. Fat makes leptin. Florant thinks insulin also may help hibernators watch their weight. Humans probably also have what it takes to regulate body fat the way marmots do, he said. "We're mammals just like the marmots, so we must have the same genes," Florant said. Very young humans may have the most in common with hibernators, said Bill Milsom, a zoologist and comparative physiologist at the University of British Columbia. Hibernators can stop breathing for long periods when cold. Golden- mantled ground squirrels may stop breathing for up to 45 minutes at a time. The animals then take a rapid series of 20 or more breaths before they halt breathing again. Young human and rat babies cooled to super low temperatures also stop breathing for a long time and enter a state similar to hibernation. The infants can recover fully once warm, Milsom said. But adult humans have long since lost that ability. If adults get too cold, not only do they stop breathing, but their hearts stop as well. Rewarming doesn't help either. "They go from being cold and dead to being warm and dead," Milsom said. Learning how hibernators control their breathing could someday lead to a better understanding of SIDS, Milsom hopes. SIDS may happen at the transition point when humans lose the ability to hibernate. When hibernators get cold, they get tough, researchers led by Hannah V. Carey at the University of Wisconsin have discovered. Because their hearts slow, hibernators don't send as much blood to their tissues. That can damage organs. Hibernating 13-lined ground squirrels have no trouble protecting their intestines when the blood supply is clamped off, Carey found. But the same animals in summer mode suffered almost as much intestinal damage as rats when blood supply to the intestines was cut off. Carey said that determining how ground squirrels protect their intestines during hibernation could lead to drugs that could enable accident victims to survive similar injuries or help preserve organs for transplant longer.